[TableGen] Remove unnecessary explicit initialization to null of a unique_ptr. NFC

llvm-svn: 238726

llvm/include/llvm/TableGen/Record.h

@@ -57,7 +57,7 @@ private:
 public:
   RecTyKind getRecTyKind() const { return Kind; }
 
-  RecTy(RecTyKind K) : Kind(K), ListTy(nullptr) {}
+  RecTy(RecTyKind K) : Kind(K) {}
   virtual ~RecTy() {}
 
   virtual std::string getAsString() const = 0;